Paper substrates and similar porous sheet substrates are commonly used for preservation of biological samples. Examples are the chemically treated FTA® and FTA® Elute papers (GE Healthcare) for preservation of nucleic acid samples and the FTA® DMPK cards and 903® cards (GE Healthcare) for preservation of blood samples. A common feature for the methods of using these substrates is that a wet biological sample (blood, buccal swabs, macerated tissue etc.) is placed on the substrate, absorbed in the porous structure and dried. If the drying is incomplete or slow, the stability of the sample may be impaired and inconsistent results may be obtained in subsequent analyses of components in the preserved samples. The standard procedure is to dry the substrate with the sample in ambient air, which leads to long drying times—up to 18 h—before complete water removal, during which time degradation and mould or bacterial growth may cause deterioration of the sample.
Several devices for preservation of samples on paper substrates have been described, e.g. the buccal cell sampling device of U.S. Pat. No. 7,748,283. The drying of the sample on the substrate in such devices is done under ambient conditions, which can be slow—particularly if the humidity is high.
U.S. Pat. No. 6,703,216 mentions that chemical heat pads can be used to evaporate interfering ethanol in gammahydroxybutyrate dipstick analyses, but this publication does not relate to preservation of biological samples and does not describe any drying of such samples.
Accordingly there is a need for a method and a device that provides improved stability and consistency in preservation of biological samples on porous sheet substrates.